<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body style="height: 3000px;">
  <div id="app">
    <button @click="showHide">{{isShow?'消失':'显示'}}</button>
    <common-head v-if="isShow"></common-head>
  </div>
  <script src="./vue.js"></script>
  <script>
    Vue.component('CommonHead', {
      template: `
        <div>
          <h1 ref="h1">我是头部组件</h1>
          {{ num }}
        </div>
      `,
      data(){
        return {
          num: 1,
          timer: null
        }
      },
      created() {
        this.timer = setInterval(()=>{
          this.num++;
          console.log(this.num)
        },1000)
      },
      mounted() {
        window.onscroll = ()=>{
          let sTop = document.documentElement.scrollTop || document.body.scrollTop;
          console.log(sTop)
        }
      },
      beforeDestroy() {
        clearInterval(this.timer)
      },
      destroyed() {
        console.log('destroyed')
      },
    })
    const vm = new Vue({
      el: '#app',
      data: {
        isShow: true
      },
      methods: {
        showHide(){
          this.isShow = !this.isShow
        }
      },
    })
  </script>
</body>
</html>